U.S. Pat. No. 4,496,395 to Croat, assigned to the assignee of this application, discloses high coercivity rare earth-iron alloys and the method of making them by melt spinning a molten mixture of the alloy precursors. An intrinsic room temperature coercivity exceeding 5 kOe was obtained with a neodymium-iron alloy in its as-quenched condition. A samarium-iron alloy having typically about 40 atomic percent samarium was also disclosed. U.S. Pat. No. 4,802,931 to Croat, also assigned to the assignee of this application, discloses the related rare earth-iron alloy further including boron. The preferred methods of forming permanent magnets from that material include over-quenching a molten mixture of the precursors by melt spinning and then annealing to promote crystal growth to the optimum size for the desired magnetic properties; alternatively the material is direct quenched to form the desired crystal sizes. An intrinsic room temperature coercivity exceeding 15 kOe was obtained along with very high remanence and high energy product. This alloy contained about 14 atomic percent of neodymium for the rare earth element. The substitution of samarium for neodymium was considered but only an intrinsic room temperature coercivity of 1,800 was achieved.
The work of Croat, discussed above, stimulated many researchers to study ternary rare earth-iron alloys in an attempt to find other useful permanent magnet materials. Compounds having the tetragonal ThMn.sub.12 structure have been identified as promising candidates. These compounds have the form REFe.sub.12-x T.sub.x where RE is a rare earth, T Si, Ti, V, Cr, Mo or W and typically x=2. The use of samarium for the rare earth has been determined to be of particular interest and coercivities of up to 2.5 kOe have been reported for melt-spun Sm.sub.8 Fe.sub.84 Ti.sub.8 and up to 3.8 kOe for mechanically alloyed Sm.sub.12 Fe.sub.80 Mo.sub.10. Thus a myriad of possible compounds and processing methods present themselves. Only a few, if any, of the possible combinations are likely to be useful permanent magnet materials.